MFC SDI: How do I create transparent SDI views

 

MFC SDI: How do I create transparent SDI views?

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Q: How do I create transparent SDI views?

A: One can make a the view of an MFC application transparent by handling 'CView::OnEraseBkgnd()' function and returning 'FALSE' instead of the default 'CView::OnEraseBkgnd()' call.

Code:

BOOL CTransparentView::OnEraseBkgnd(CDC* pDC) {  // TODO: Add your message handler code here and/or call default  return FALSE;//  return CView::OnEraseBkgnd(pDC);}

But this will not give a real transparent window, since the original view background will be dragged along while moving the application window. To overcome this, I have handled 'OnMove()' and 'OnSize()' functions of 'CMainFrame' class to update the view to reflect the real background, by repainting the view each time the application window is moved / sized.

Code:

void CMainFrame::OnMove(int x, int y) {  CFrameWnd::OnMove(x, y);    // TODO: Add your message handler code here  RepaintView();}void CMainFrame::OnSize(UINT nType, int cx, int cy) {  CFrameWnd::OnSize(nType, cx, cy);    // TODO: Add your message handler code here  RepaintView();}

I have defined a function 'RepaintWindow()' as part of the 'CMainFrame' class and implemented to repaint the view with correct background information.

Code:

void CMainFrame::RepaintView(){  // Gets current view  CView* pView = GetActiveView();  if (pView)    // Valid view  {    // Hides view to get background    ShowWindow(SW_HIDE);    // Gets desktop device context    HDC hDC = ::GetDC(NULL);    if (hDC)  // Valid device context handle    {      // Get clients rectangle in screen coordinates      CRect Rect;      pView->GetClientRect(Rect);      pView->ClientToScreen(Rect);      // Gets device context for current view      CClientDC DC(pView);      // Pastes background to view      ::BitBlt(DC.m_hDC, 0, 0, Rect.Width(), Rect.Height(),        hDC, Rect.left, Rect.top, SRCCOPY);      // Releases desktop device context      ::ReleaseDC(NULL, hDC);    }    // Shows view with right background info    ShowWindow(SW_SHOW);  }}

At present, this is implemented for SDI application. With little modification (for updating all views), this methodology can be extended for MDI applications as well.